Drive means for snowmobile devices

ABSTRACT

A drive and suspension assembly for snowmobiles or similar vehicles having endless track propulsion means, wherein the angular disposition of the base of the track is responsive to increases in torque being applied to the drive sprockets. The snowmobile vehicles are provided with conventional frames with forward and rear mounts for attaching the drive and suspension assembly to the frame, and means are provided on the drive and suspension assembly for receiving a drive track. Forward drive sprocket means are provided for delivering power to the track and rear idler sprockets are provided to support the track and define upper and lower spans in the track. The drive and suspension assembly comprises an elongated generally longitudinally disposed suspension support means having a forward end portion journaled to the forward frame mount and being adapted for pivotal motion thereabout. A rearwardly disposed mounting means is provided including a generally transversely disposed mounting shaft having stabilizing means resiliently coupling the rear mounting shaft to the rear frame mount, with the stabilizer means normally urging the suspension support means away from the rear frame mount. The stabilizer means normally include shock absorbers and coil springs. The suspension support means further has a rear pivotal coupling means disposed adjacent the rear portion thereof, the rear pivotal coupling means being attached to longitudinally arranged support rails for the lower span of the drive track. The longitudinal support rails are journaled with the rear pivotal coupling means of the suspension support, with lug means being provided extending upwardly from the support rail means for mounting the rear axle shaft for the rear idler sprockets. The longitudinal support rail means further are provided with track contacting means which support the inner surface of the lower span of the drive track to define a running surface for the lower span.

United States Patent Hendrickson [54] DRIVE MEANS FOR SNOWMOBILE DEVICES[72] Inventor: George Vernon liendrlckson, Twin Valley, Minn.

[73] Assignee: Viking Snowmobiles, Inc., Twin Valley, Minn.

[22] Filed: July 23, 1971 211 Appl. No.: 165,451

[52] US. Cl. Q. ..180/5 R, 305/27, ISO/9.54 [51] Int. Cl. ..B62m 27/02,862d 55/10 [58] Field of Search ..l80/5 R, 9.54; 305/27 [56] ReferencesCited UNITED STATES PATENTS 1,276,035 8/1918 Crane ..180/5 R 1,336,8324/1920 Fuchs ..305/27 3,485,312 12/1969 Swenson ..180/5 R 3,613,81110/1971 Brandli ..180/5 R 3,613,810 10/1971 Hetteen ..180/5 R PrimaryExaminer-Richard J. Johnson Attorney-Orrin M. l-laugen [S 7] ABSTRACT Adrive and suspension assembly for snowmobiles or similar vehicles havingendless track propulsion means, wherein the angular disposition of thebase of the track is responsive to increases in torque being applied tothe drive sprockets. The snowmobile vehicles [451 Oct. 31, 1972 areprovided with conventional frames with forward and rear mounts forattaching the drive and suspension assembly to the frame, and means areprovided on the drive and suspension assembly for receiving a drivetrack. Forward drive sprocket means are provided for delivering power tothe track and rear idler sprockets are provided to support the track anddefine upper and lower spans in the track. The drive and suspensionassembly comprises an elongated generally longitudinally disposedsuspension support means having a forward end portion journaled to theforward frame mount and being adapted for pivotal motion thereabout. Arearwardly disposed mounting means is provided including a generallytransversely disposed mounting shaft having stabilizing meansresiliently coupling the rear mounting shaft to the rear frame mount,with the stabilizer means normally urging the suspension support meansaway from the rear frame mount. The stabilizer means normally includeshock absorbers and coil springs. The suspension support means furtherhas a rear pivotal coupling means disposed adjacent the rear portionthereof, the rear pivotal coupling means being attached tolongitudinally arranged support rails for the lower span of the drivetrack. The longitudinal support rails are journaled with the rearpivotal coupling means of the suspension support, with lug means beingprovided extending upwardly from the support rail means for mounting therear axle shaft for the rear idler sprockets. The longitudinal supportrail means further are provided with track contacting means whichsupport the inner surface of the lower span of the drive track to definea running surface for the lower span.

14 Claims, 10 Drawing Figures BACKGROUND OF THE INVENTION The presentinvention relates generally to a drive and suspension assembly forvehicles having endless track propulsion means, or segments coupledtogether to form an endless track, and more specifically to a drive andsuspension assembly for a self-propelled snowmobile structure. The driveand suspension assembly of the present invention provides a drivesurface angle of attack which is responsive to the torque being appliedto the endless track. As the torque increases, the forward portion ofthe drive and suspension assembly moves downwardly away from the vehiclein response to the increase in torque such as, for example, duringacceleration or climbing. The function is reversed upon deceleration.Furthermore, the drive and suspension assembly is capable of providing asmooth ride under a variety of operating conditions, withthe tracksurface being arranged to contact the running surface at all times. Thestructureis further designed to provide constant tension particularlyalong the bottom span in the track at all times, regardless of thedisposition of the track within the suspension assembly.

The drive and suspension assembly of the present invention enables thestructure to move effectively without excessive slipping or skiddingunder diflicult driving conditions, such as, for example, during racingevents and the like. The improved drive and suspension assembly of thepresent invention provides for optimum contact between the drive surfaceof the endless track and the running surface. Means are also providedfor adjusting the spring force utilized in the suspension, so as toprovide a smooth ride under a variety of conditions. All of theseadvantages are achieved with the use of an extremely rugged and durablestructure.

SUMMARY OF THE INVENTION Therefore, it is primary object of the presentinvention to provide an improved drive and suspension assembly forsnowmobile structures having endless track propulsion means, wherein theangular disposition of the running surface of the track is responsive tothe torque being applied to the track.

It is a further object of the present invention to pro-' vide animproved drive and suspensionassembly for snowmobile vehicles havingendless track propulsion means wherein the suspension means is providedwith a pair of longitudinal support rails which define the runningsurface for the lower span of theendless track, these support railsbeing pivotal in response to the torque being appliedto the drive track.

It is yet a further object of the present invention to provide animproved drive and suspension assembly for vehicles having endless trackpropulsion means wherein longitudinally disposed support rails areprovided for the lower span of the endless track, and wherein thesupport rails provide a base running surface for the track responsive tothe drive torque being applied to the endless track, and wherein thedrive and suspension means is adapted to provide a smooth ride generallyfree from shock experienced over uneven terrain.

It is yet a further object of the present invention to provide animproved drive and suspension assembly for vehicles having endless trackpropulsion means wherein improved means for supporting the lower surfaceof the endless track are provided, and wherein controlled resilient biasis available between the frame of the vehicle structure and the driveand suspension assembly.

Other and further objects of the present invention will become apparentto those skilled in the art upon a study of the following specification,appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of asnowmobile vehicle utilizing the improved drive and suspension assemblyof the present invention, with the drive and suspension assembly beingshown partially in phantom;

FIG. 2 is a detail horizontal sectional view on 'a slightly enlargedscale, and being taken along the line and in the direction of arrows 2-2of FIG. I, with the upper span of the endless track being cut away;

FIG. 3 is a vertical sectional view taken along the line and in thedirection of the arrows 3-3 of FIG. 2;

FIG. 4 is a detail sectional view on a slightly enlarged scale, andtaken along the line and in the direction of the arrows 4-4 of FIG. 2;

FIG. 5 is a view similar to FIG. 4, but on a slightly reduced scale, andillustrating the drive and suspension assembly in collapsed disposition;

FIG. 6 is a detail plan view of the forward portion of the drive andsuspension assembly, and illustrating the manner of coupling thisportion of the assembly to the frame mount;

FIG. 7 is a detail vertical sectional view taken along the line and inthe direction of the arrows 7-7 of FIG.

FIG. 8 is a vertical sectional view similar to FIG. 3, and illustratinga modified configuration of the drive and suspension assembly of thepresent invention utilizing a slide rail structure in lieu of the bogiewheel structure illustrated in FIGS. 1-7;

FIG. 9 is a detail fragmentary elevational view of a portion of amodified form of stabilizer structure used in coupling the support railsto the main longitudinal shaft of the assembly; and

FIG. 10 is a detail fragmentary plan view of the structure of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT With particular attention beingdirected to FIG. 1 of the drawings, the self-propelled snowmobilevehicle generally designated 10 includes a frame structure and housing11 supported upon a forward ski structure 12 which is steerable throughthe steering column assembly l3 and coupled to the frame 11 through theski mounting arrangement 14. The steering portion of the snowmobilestructure is conventional, and snowmobile vehicles having thisarrangement of components are, of course, available commercially. Thedrive and suspension assembly shown generally at 16 is coupled to theframe 11 at the forward mount 17, and the rear mount 18. The drive trackis shown at 19, and is supported by a forward drive sprockets 20-20 andrear idler sprockets 21-21. As is indicated, the forward drive sprockets20-20 are journaled on front axle shaft 23,

while rear idler sprockets 21-21 are supported on rear axle shaft 24. Asis illustrated in FIGS. 1 and 3, drive belt 27 is utilized to providethe driving torque from the engine 28 through transmission assembly 29.Also, as is conventional, main drive belt 30 is utilized to deliverpower from engine 28 to transmission 29.

Endless drive track 19, in the operational configuration, has an upperspan segment 19A, and a lower ground or surface contacting segment 198.As has been indicated hereinbefore, the drive and suspension assembly ofthe present invention provides a means for controlably modifying theangle or running disposition of the lower span19B of track 19 inresponse to the torque being delivered to belt 19 at the forward drivesprockets. As this torque increases, that portion of the drive andsuspension assembly in contact with the lower span portion 198 of belt19 moves downwardly against the running surface, so as to provideimproved traction under conditions of acceleration and climb. Thisshifting of the angle or running disposition of the lower span of track19 is accomplished without modifying the tension in the track. It willalso be observed, particularly in FIGS. 1, 4 and that the rear idlersprockets are normally elevated from the running surface. This enhancesthe ability of the structure to turn about a shorter radius, and tendsto eliminate fishtailing structure includes an elongated generallylongitudinally .disposed suspension support means 35 which is in theform of a shaft or the like, and which is centrally disposed. Theforward end portion of support means 35 is journaled to the forwardframe mount 17, such as in the bushing arrangement shown at 36. Thisarrangement provides for pivotal motion of support shaft 35 about mount17. Support shaft 35 is coupled to transverse mounting shaft 38,mounting shaft 38 being provided with stabilizer means in .the form oflaterally arranged shock absorbers 40 and 41, along with resilientspring members 42 and 43. These stabilizing means in the form of shockabsorbers 40 and 41, and resilient spring members 42 and 43, are coupledto rear frame mount 18, as is indicated in FIG. 2, with one end bracketof each of shock absorbers 40 and 41 being coupled directly to framemount 18, and with the free ends of coil spring members 42 and 43 beingurged against the underside portion of frame mount 18. Tension insprings 42 and 43 is adjustably controlled by means of clamping buckles45 and 46, with one end portion of buckles 45 and 46 being secured tomounting ears 47-47, and with the hook end portion of buckles 45 and 46engaging the claw portion of the spring, such as is shown at 49 in FIG.3.

The rear portion of suspension support shaft 35 is provided with aninverted generally U-shaped slide member 50, which circumscribes theouter'circum- 7 ends of yoke 51, such as are shown at 52 and 53, en-

gage the rear leg portions of support rails 55 and 56, in the mannerillustrated in FIGS. 2 and 4. As is indicated, a pivotal engagement isused to couple member 51 to each of the rails 55 and 56 in order topermit relative pivotal rotation between these portions of theapparatus. A portion of the detail is illustrated in FIG. 3 as well.

Further details of the longitudinally disposed suspension support meansare illustrated in FIGS. 6 and 7. As is indicated in these figures,forward spring bias member 58 is utilized to normally bias support rails55 and 56 downwardly and away from the longitudinally disposedsuspension support means 35. As is apparent in FIGS. 2 and 3, two suchspring members are provided, these being shown at 58 and 59. Bucklemembers 60 and 61 are utilized to control the tension in spring members58 and 59, with buckles 60 and 61 being adjustable in their dispositionthrough brackets 62 and 63. As is indicated in FIG. 3, a claw portion ofspring 58, such as is illustrated at 64, engages the eye portion ofbuckle 61.

In order to controllably guide the motion of support rails 55 and 56relative to the suspension support means 35, a pair of rod and sleeveassemblies are provided as at 66, these assemblies having a pivotalmounting point at or along shaft 35, and a sleeve member as at 68. Thus,lateral displacements of rails 55 and 56 from support means 35 will beavoided. A modified form of controlable guide is illustrated in FIG. 9.

' In order to accommodate the relative motion between support rails 55and 56, and suspension support means 35, sleeve guides are also providedfor springs 58 and 59, as shown at and 71. Such an arrangement enhancesthe ability of the unit to respond to the torque being applied to thedrive track, and also to respond to changes in terrain. The adjustabletension feature is utilized to match the stiffness of the springs 58 and59 to the load being carried.

With continued attention being directed to FIGS. 6 and 7 of thedrawings, the adjustment for longitudinal length of the drive andsuspension assembly is illustrated. This adjustment feature permitsaccommodation for variations in track length which may be encountered insnowmobile structures. A locking collar is shown at 73, collar 73 beingsecured by bolts 74-74 to studs 75-75. Shims are provided as at 76 toaccommodate the length requirements of the longitudinally disposedsuspension support means 35. Shims 76 are preferably large rubbergrommets, and in addition to controlling the axial length of the system,also permit a certain amount of lateral flexing to occur in thestructure. This lateral flexing enhances the ability of the unit torespond smoothly to uneven surface terrain and to avoid pulling to oneside or the, other in response to uneven terrain.

Also, in order to control the length of the drive suspension, the boresformed in the walls of the tunnel in order to accommodate the mountingpoints 17 and 18, may be in the form of elongated slots. Such slots willpermit additional adjustment of the axial length of the suspensionsystem. In order to secure such a system in place, conventional jam nutsmay be employed to achieve the adjustment feature.

Attention is now re-directed to FIGS. 3 and 4 of the drawings whereinthe details of longitudinal support rail means are best illustrated. Inthis connection, the individual rails and 56 are provided with lug meanswhich extend upwardly from the rear pivotal coupling with segments'52and 53 of yoke member 51. As is indicated in FIG. 2, for example,support rail 56 is provided with its lug member 81. At the upper end ofeach of lug members 80 and 81 there is provided means for mounting therear axle shaft 24, rear axle shaft 24 being provided to journal andotherwise accommodate rotation of rear idler sprockets,2l--2l. Thisfeature is, of course, illustrated in FIGS. 3 and 4, with additionaldetail being supplied from FIG. 2. With the offset provided between thepivotal mounting of segments 52 and 53 to the support rails 55 and 56and. the axle shaft 24, pivotal rotation is accordingly provided acrossthe moment arm existing between the suspension support means and therear-axle shaft 24. This moment arm provides for pivotal rotationalmotion between the longitudinally disposed suspension support means andthe support rails 55 and 56 in accordance with the arcuate arrow shownat 83.

As is apparent from the illustrations in FIG. 3 and 4, the verticaldisposition of the axle shaft 24 is actually ahead or forwardly of theaxis of portions 52 and 53 of yoke 51. Preferably, this leadingdisposition should be in the area of about 6 of are, so as to eliminatethe tendency for the pivotal motion to arrive at a top-deadcenterdisposition. Thus, the motion will be smooth and uniform between thesuspension support means and the support rail means.

By way of functional response, as increased torque is being delivered tothe front drive sprockets 20-20, tension in the upper span 19A of belts19 increases, thus delivering a forwardly directed force to axle shaft24. This forwardly directed force, in turn, finds response and reactionby a downward thrust on each of support rails 55 and 56. This downwardlydirected thrust is in the clockwise direction of double-ended arrow 83,and results in an increase in traction between the running surface andthe lower surface 193 of belt 19. This motion is accomplished withoutmodifying or changing tension in the track. Thus, as the rear idlersmove forward, the motion in the support rails takes up any slack thatmay develop due to forward rocking of rear idlers 21--21. Each ofsupport rails 55 and 56 are provided with track contacting means whichsupport the inner surface of the lower span 19B of belt 19, thesesupporting members being in the form of longitudinally spaced bogiewheels -98 inclusive. While wheels 85-98 have been referred to as bogiewheels, it will be appreciated that these wheels are in effect idlerwheels which maintain a force against the inner surface of the belt soas to cause the belt to conform to the profile desired. If desired, thewheels 85-98 may be spring-loaded so as to exert a resilient forceagainst the inner surface of the belt structure. Therefore, for purposesof this application, the term bogie wheels" is used in a comprehensivesense and includes both resiliently biased idler wheels as well as fixedidler wheels. As is apparent from the illustrations in FIG. 2, wheels 85and 86 are joumaled on transverse shaft 99, while wheels 87 and 88 areindependently joumaled on shaft 100. Additional transverse bogie wheelshafts are shown at 101 and 102, with independentshafts being providedfor bogie wheels and 96 at 103, and for With attention being directed toFIG. 5, the disposition of the drive and suspension assembly is shownthere in collapsed form. This disposition would be expected to occurupon operation over rough terrain, when a downward thrust is applied tothe drive and suspension assembly from the frame of the vehicle. Thesystem is capable of accommodating such motion without difficulty, andhence it will be appreciated that a relatively smooth ride can beobtained from the structure when utilizing this drive and suspensionassembly.

Attention is now directed to FIG. 8 of the drawings wherein a modifiedform of the structure is illustrated utilizing slide rails rather thanbogie wheels. These slide rails are shown at 110, and have an undersurface 111 which makes contact with the inner surface of the lower span19B of belt 19, such as at 112. Suitable low friction surfacing isprovided for slides 110, such as, for example, Teflon, nylon, or thelike. Such coatings may be utilized to reduce the friction which mayotherwise exist between the belt and the slides. The individual slidesare coupled to the support rails 55 and 56 by means of mounting lugs113, 114 and 115. In the embodiment of FIG. 8, forwardly disposed bogiesare normally utilized, such as are illustrated at 98, these bogies beingthe same as those utilized in the modification illustrated in FIgS. l-7.The other features of the slide rail embodiment are the same as thosepreviously discussed in connection with the bogie wheel structure, andthe function of the structures are, accordingly, substantiallyidentical. With the lower periphery of the rear idlers being elevatedfrom the normal running surface, and with the arrangements asillustrated herein, it will be apparent that a constant pressure willexist along the surface of the track throughout the contacting surface.Such an arrangement equalizes the forces throughout the contactingextent of the track and hence enhances the smoothness of the ride, aswell as the serviceability of the track.

and 121 include a pair of arm elements 124 and 125" converging upon acommon pivotal point 126 such as a pinned bushing, these arm elementsbeing, in turn, coupled to the rail structure along bogie wheel axlehousing 127 as at 128, axle 127 being secured to the support rails. Stoplug 129 prevents over-centering of the arm elements. While this latterportion of the hinge support means has been described with regard'to abogie wheel structure, it will be appreciated that the same structureapplies to the slide rail structure shown in FIG. 8.

it will be appreciated that the structure of the present invention isparticularly adapted for use with a snowmobile structure having a drivesprocket at the forward end of the endless drive track. The unit can beadapted for functioning with other drive systems, by a mere reversal ofcertain components. Such a modification will, of course, be readilyapparent to those skilled in the art, and may be made without departingfrom the aspects of the structure illustrated herein.

lclaim:

l. A drive and suspension assembly for vehicles having endless drivetrack propulsion means, the vehicle having a frame with forward and rearmounts for attaching the drive and suspension assembly to the frame,means for receiving a drive track on said drive and suspension assembly,and forward drive sprocket means for delivering power to said track, andrear idler sprocket means supporting said track and being journaled onrear axle shaft means, said sprockets defining an upper and lower spanin said drive track, said drive and suspension assembly comprising:

a. an elongated generally longitudinally disposed suspension supportmeans having a forward end portion journaled tosaid forward frame mountand adapted for pivotal motion thereabout, and with a rearwardlydisposed mounting means including a generally transversely disposedmounting shaft having stabilizing means resiliently coupling said rearmounting shaft to said rear frame mount with said stabilizer meansnormally urging said longitudinal suspension support means away fromsaid rear frame mount, said suspension support means having a rearpivotal coupling means disposed adjacent the rear portion thereof;

. longitudinal support rail means for the lower span of said drive trackjournaled with said rear pivotal coupling means, said support rail meanshaving lug means extending from said support rail means for mountingsaid rear axle shaft means thereto, the axis of said rear axle shaftbeing generally parallel to and spaced upwardly from said rear pivotalcoupling means; and

. said longitudinal support rail means having track contacting meanssupporting the inner surface of the lower span of said endless drivetrack and defining a running surface for said lower span, said supportrail means being adapted for arcuate pivotal rotation with said lugmeans about said rear pivotal coupling.

2. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that the axis of said rear axle shaft isdisposed normally forwardly of the axis of said rear pivotal couplingmeans.

3. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said stabilizer means includes a pairof elongated shock absorbers coupling said rear frame mount to saidlongitudinal support rails.

4. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said longitudinal support railsinclude a pair of generally parallelly disposed rails disposed adjacentthe lateral outer edges of said endless track.

5. The drive and suspension assembly as defined in cl im4bein a icul rlha d' th ral ity of bogi e zvl 'lieels 2m s ecii i eii t ri airl longitti ll' lgl support rails at longitudinally spaced intervals therealong.

6. The drive and suspension assembly as defined in claim 4 beingparticularly characterized in that slide rail means are disposed alongthe lower surface of said support rails.

7. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said resilient means coupling saidrear mounting shaft to said rear frame mount includes a coil spring, andmeans are provided for adjusting a bias force normally urging saidsuspension support means away from said rear frame mount.

8. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that forward stabilizer means are providedfor controlling the lateral disposition of said support rails relativeto said longitudinally disposed suspension support means.

9. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that second resilient means are disposedadjacent the forward end of said support rail means for normally urgingthe forward end of said support rail means downwardly away from saidforward frame mount.

10. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that adjustment means are provided forcontrolling the length of said longitudinally disposed suspensionsupport means.

11. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said suspension support meansincludes an axially disposed shaft extending a substantial portion ofthe distance between said forward and rear frame mounts.

12. The drive and suspension assembly as defined in claim 11 beingparticularly characterized in that said suspension support meansincludes a yoke member disposed at the rear portion thereof, with saidyoke member coupling said suspension support means to said lug means.

13. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that the pivotal motion of said rear axleshaft and said support rails about said rear pivotal coupling isarranged to maintain substantially constant tension in said lower drivetrack span.

14. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said elongated generallylongitudinally disposed suspension support means is adapted for pivotalmotion in two coordinates of planes, the first being about said forwardframe mount, and the second being about the central axis of saidlongitudinally disposed suspension support means.

1. A drive and suspension assembly for vehicles having endless drivetrack propulsion means, the vehicle having a frame with forward and rearmounts for attaching the drive and suspension assembly to the frame,means for receiving a drive track on said drive and suspension assembly,and forward drive sprocket means for delivering power to said track, andrear idler sprocket means supporting said track and being journaled onrear axle shaft means, said sprockets defining an upper and lower spanin said drive track, said drive and suspension assembly comprising: a.an elongated generally longitudinally disposed suspension support meanshaving a forward end portion journaled to said forward frame mount andadapted for pivotal motion thereabout, and with a rearwardly disposedmounting means including a generally transversely disposed mountingshaft having stabilizing means resilieNtly coupling said rear mountingshaft to said rear frame mount with said stabilizer means normallyurging said longitudinal suspension support means away from said rearframe mount, said suspension support means having a rear pivotalcoupling means disposed adjacent the rear portion thereof; b.longitudinal support rail means for the lower span of said drive trackjournaled with said rear pivotal coupling means, said support rail meanshaving lug means extending from said support rail means for mountingsaid rear axle shaft means thereto, the axis of said rear axle shaftbeing generally parallel to and spaced upwardly from said rear pivotalcoupling means; and c. said longitudinal support rail means having trackcontacting means supporting the inner surface of the lower span of saidendless drive track and defining a running surface for said lower span,said support rail means being adapted for arcuate pivotal rotation withsaid lug means about said rear pivotal coupling.
 2. The drive andsuspension assembly as defined in claim 1 being particularlycharacterized in that the axis of said rear axle shaft is disposednormally forwardly of the axis of said rear pivotal coupling means. 3.The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said stabilizer means includes a pairof elongated shock absorbers coupling said rear frame mount to saidlongitudinal support rails.
 4. The drive and suspension assembly asdefined in claim 1 being particularly characterized in that saidlongitudinal support rails include a pair of generally parallellydisposed rails disposed adjacent the lateral outer edges of said endlesstrack.
 5. The drive and suspension assembly as defined in claim 4 beingparticularly characterized in that a plurality of bogie wheels aresecured to said longitudinal support rails at longitudinally spacedintervals therealong.
 6. The drive and suspension assembly as defined inclaim 4 being particularly characterized in that slide rail means aredisposed along the lower surface of said support rails.
 7. The drive andsuspension assembly as defined in claim 1 being particularlycharacterized in that said resilient means coupling said rear mountingshaft to said rear frame mount includes a coil spring, and means areprovided for adjusting a bias force normally urging said suspensionsupport means away from said rear frame mount.
 8. The drive andsuspension assembly as defined in claim 1 being particularlycharacterized in that forward stabilizer means are provided forcontrolling the lateral disposition of said support rails relative tosaid longitudinally disposed suspension support means.
 9. The drive andsuspension assembly as defined in claim 1 being particularlycharacterized in that second resilient means are disposed adjacent theforward end of said support rail means for normally urging the forwardend of said support rail means downwardly away from said forward framemount.
 10. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that adjustment means are provided forcontrolling the length of said longitudinally disposed suspensionsupport means.
 11. The drive and suspension assembly as defined in claim1 being particularly characterized in that said suspension support meansincludes an axially disposed shaft extending a substantial portion ofthe distance between said forward and rear frame mounts.
 12. The driveand suspension assembly as defined in claim 11 being particularlycharacterized in that said suspension support means includes a yokemember disposed at the rear portion thereof, with said yoke membercoupling said suspension support means to said lug means.
 13. The driveand suspension assembly as defined in claim 1 being particularlycharacterized in that the pivotal motion of said rear axle shaft andsaid support rails about said rear pivotal coupling is arranged tomaintain substantially constant tension in said lower drivE track span.14. The drive and suspension assembly as defined in claim 1 beingparticularly characterized in that said elongated generallylongitudinally disposed suspension support means is adapted for pivotalmotion in two coordinates of planes, the first being about said forwardframe mount, and the second being about the central axis of saidlongitudinally disposed suspension support means.